1. Technical Field of the Invention
This invention relates to temperature monitoring systems and, more particularly, to a temperature tag that is placed on shipped goods to monitor and record the internal temperature of a shipping container at a defined sampling rate during shipment of the goods.
2. Description of Related Art
Some goods, such as food items, require that their temperature be maintained within an acceptable range during shipping and handling. In the food industry today, foods must be shipped for long distances from farms or processing plants, to distribution centers, and then to their final destinations at restaurants or grocery stores. In many cases, the trips may take several days and require that the food be refrigerated or frozen during the trip. It is important for the freshness and safety of the food that the temperature be maintained in a safe range throughout the trip. For some foods, particularly meats, fish, and poultry, even small temperature excursions of short duration outside the safe range can be dangerous since these foods tend to spoil quickly.
It is known in the prior art for distributors of frozen and refrigerated goods to place temperature sensitive stickers on the outside of the boxes in which the food is shipped. If the temperature on the outside of a box rises above a threshold limit at any time during the trip from the distribution center to the final destination, the sticker on the outside of the box changes color. At the final destination, the receiver can check the stickers on the outside of the boxes to ensure that none of them have been exposed to excessive temperatures.
The disadvantage of temperature sensitive stickers is that they do not provide enough information to accurately determine whether the food inside the boxes has been adversely affected by temperature changes. A short duration temperature rise on the outside the box may cause the sticker to change colors without affecting the food inside the box. This may occur in hot climates, for example, when moving the boxes from a freezer to a refrigerated truck. No harm is caused to the food unless the duration of the rise in temperature is long enough to begin thawing the food. The temperature sensitive stickers, however, do not give a history or duration of the temperature variations.
It would be advantageous to have a temperature tag that is placed on shipped goods to monitor and record the temperature inside the shipping container at a defined sampling rate during shipment of the goods. A reader device at the final destination could then interrogate the tag and present the internal temperature data to a user. The present invention provides such a temperature tag and a system that includes the tag and the reader device.